[PATCH v2] qemu: process: Improve update of maximum baloon state at startup

[Peter Krempa <pkrempa@xxxxxxxxxx>]

In commit 641a145d73fdc3dd9350fd57b3d3247abf101c05 I've added code that
resets the ballon memory value to full size prior to resuming the vCPUs
since the size certainly was not reduced at that point.

Since qemuProcess start is used also in code paths with already booted
up guests (migration, save/restore) the assumption is not entirely true
since the guest might already been running before.

This patch adds a function that queries the monitor rather than using
the full size since a balloon event would not be reissued in case we are
recovering a saved migration state.

Additionally the new function is used also when reconnecting to a VM
after libvirtd restart since we might have missed a few ballon events
while libvirtd was not running.
---
 src/qemu/qemu_process.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index ba84182..13b1696 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2065,6 +2065,38 @@ qemuProcessReconnectRefreshChannelVirtioState(virQEMUDriverPtr driver,


 static int
+qemuProcessRefreshBallonState(virQEMUDriverPtr driver,
+                              virDomainObjPtr vm,
+                              int asyncJob)
+{
+    unsigned long long balloon;
+    int rc;
+
+    /* if no balloning is available, the current size equals to the current
+     * full memory size */
+    if (!vm->def->memballoon ||
+        vm->def->memballoon->model == VIR_DOMAIN_MEMBALLOON_MODEL_NONE) {
+        vm->def->mem.cur_balloon = virDomainDefGetMemoryActual(vm->def);
+        return 0;
+    }
+
+    if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)
+        return -1;
+
+    rc = qemuMonitorGetBalloonInfo(qemuDomainGetMonitor(vm), &balloon);
+    if (qemuDomainObjExitMonitor(driver, vm) < 0)
+        rc = -1;
+
+    if (rc < 0)
+        return -1;
+
+    vm->def->mem.cur_balloon = balloon;
+
+    return 0;
+}
+
+
+static int
 qemuProcessWaitForMonitor(virQEMUDriverPtr driver,
                           virDomainObjPtr vm,
                           int asyncJob,
@@ -3779,6 +3811,9 @@ qemuProcessReconnect(void *opaque)
     if (qemuProcessReconnectRefreshChannelVirtioState(driver, obj) < 0)
         goto error;

+    if (qemuProcessRefreshBallonState(driver, obj, QEMU_ASYNC_JOB_NONE) < 0)
+        goto error;
+
     if (qemuProcessRecoverJob(driver, obj, conn, &oldjob) < 0)
         goto error;

@@ -4922,7 +4957,8 @@ int qemuProcessStart(virConnectPtr conn,
     /* Since CPUs were not started yet, the ballon could not return the memory
      * to the host and thus cur_balloon needs to be updated so that GetXMLdesc
      * and friends return the correct size in case they can't grab the job */
-    vm->def->mem.cur_balloon = virDomainDefGetMemoryActual(vm->def);
+    if (qemuProcessRefreshBallonState(driver, vm, asyncJob) < 0)
+        goto cleanup;

     VIR_DEBUG("Detecting actual memory size for video device");
     if (qemuProcessUpdateVideoRamSize(driver, vm, asyncJob) < 0)
-- 
2.4.1

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